For decades, soon after the first of the matrix metalloproteinases (MMPs), known as collagenase-1 or MMP-1, was discovered in the early 1960s (1), academics and industry have been trying to develop safe and effective pharmaceuticals to inhibit these calcium- and zinc-dependent neutral proteinases which are expressed and activated in excessive levels during a variety of diseases (see (2) and (3) for reviews). The rationale for this drug development strategy lies in the fact that collagen and the other connective tissue constituents: (a) are collaboratively degraded by these MMPs (now numbering more than 25 genetically distinct types, “22 found in the human genome” (2)); and (b) are found virtually everywhere in the body (e.g., skin, bone, tendons and ligaments, cornea of the eye, cartilage of the joints), and the excessive destruction of these constituents is a key event in the pathogenesis of numerous diseases ranging from inflammatory conditions (e.g., rheumatoid arthritis, atherosclerosis, periodontitis), to metabolic bone diseases (e.g., postmenopausal osteoporosis, diabetes-induced osteopenia), to cancer invasion, metastasis and angiogenesis (2, 4).
Matrix metalloproteinases (MMPs) are a collective of over thirty zinc-containing endopeptidases that include the gelatinases, stromelysins, and collagenases, released as inactive zymogens and becoming active only when the propeptide is cleaved (5). The gelatinases include MMP-2 and MMP-9, and the stromelysins include MMP-3, -7, 10, and -11. The collagenases include MMP-1, -8, and -13 (5). The MMPs, when constitutively expressed or induced by pro-inflammatory agents, such as cytokines, hormones, bacterial products, endotoxins, among others, can degrade all components of the extracellular matrix (5). Under physiological conditions, MMPs are regulated by endogenous inhibitors, particularly the tissue inhibitors of metalloproteinases (TIMPs) (5, 6a).
Aberrant MMP activity and expression has been implicated in a number of pathological conditions, including rheumatoid arthritis (RA), osteoarthritis (OA), metastases, periodontal disease, angiogenesis, emphysema, multiple sclerosis (5), and cardiovascular disease, such as atherosclerosis, myocardial infarction, arterial restenosis after angioplasty and aneurysm development (6a). Recent research has also implicated MMPs in asthma attacks, chronic obstructive pulmonary disease, and premature skin aging (6a) and inflammatory skin disease (6b, 6c). Their involvement in the epidermal growth factor-receptor activation pathway leading to cardiac hypertrophy has also been reported (6a). It is believed that an imbalance between the active enzymes and their natural inhibitors leads to the accelerated destruction of connective tissue and the potential for using specific enzyme inhibitors as therapeutic agents to redress this balance has led to intensive research focused on the design, synthesis and molecular deciphering of low-molecular-mass inhibitors of this family of proteins (7).
At least 56 MMP inhibitors have been pursued as clinical candidates since the late 1970's, and as of 2006, only 1 inhibitor, a sub-antimicrobial (low-dose) doxycycline formulation (Periostat® for periodontal disease), has been approved (8). Early clinical studies with other known MMP inhibitors, in particular a series of hydroxamic acids, have revealed a severe adverse side-effect frequently referred to as the musculoskeletal syndrome (MSS), which is a tendonitis-like fibromyalgia (8). In subsequent MMP inhibitor clinical trials, efforts to avoid MSS coupled with an inability to assess the therapeutic index (ie., the ratio between the dose required for efficacy vs. toxicology), may have resulted in dose selection beneath the minimal effective dose, hampering MMP inhibitor development (8).
Therefore, there is a need for the development of new MMP inhibitors.
Curcumin (diferuloylmethane, FIG. 1), the major component in curcuma/turmeric, is an antioxidant polyphenol from the plant Curcuma longa and is commonly used as a spice component. Curcumin has been used to treat inflammation and exerts antiproliferative and proapoptotic effects against various tumors in vitro and in vivo, and it has been found to suppress carcinogenesis of the breast and other organs (9, 10). Bachmeier and coworkers have reported downregulation of the inflammatory cytokines CXCL1 and CXCL2 in breast cancer cells via NFκB (9). Oral curcumin efficacy in vivo has been shown in models for many conditions with oxidative damage and inflammation, including many types of cancer, diabetes, atherosclerosis, arthritis, stroke, peripheral neuropathy, inflammatory bowel disease, and brain trauma (11). Curcumin, along with its tetrahydro derivative, tetrahydrocurcumin (THC, FIG. 1.), has been shown to inhibit IL-1β in an acute brain inflammation model while curcumin was more effective than THC in attenuating plaque pathogenesis in studies of curcumin efficacy in models of neuroinflammation, which is implicated in the pathogenesis of many neurodegenerative disorders, including Alzheimer's disease (AD) (11).
Curcumin has also been shown to inhibit MMPs. Curcumin (at 15 μM concentration) has been observed to exert a significant inhibitory effect on MMP-2 activity which was not reversible even after cells were grown for 28 days without curcumin (12). It is known that highly metastatic cells become less aggressive when MMP-2 expression or activity is reduced and previous studies have also shown that curcumin reduces MMP-2 expression in breast carcinoma cell lines (12). This reduction of MMP-2 activity could be an important reason for anti-metastatic property of curcumin (12). In addition, curcumin has also been shown to inhibit MMP-9 expression in human astroglioma cells (13). Analogues and derivatives of curcumin have previously been described for use against various cancers (14, 15, 16, 17) as well as pancreatitis (18).
While curcumin has been shown to have multiple beneficial effects, poor oral absorption of curcumin in both humans and animals has raised several concerns that this may limit its clinical impact (11).
Herein, novel chemically-modified curcumins as inhibitors of matrix metalloproteinases and pro-inflammatory cytokine production are disclosed.